Synthesis and thermodynamic data of acetate-containing giorgiosite – a novel hydrated magnesium carbonate

Organic additives play important roles in enhancing the formation of Mg‑carbonates and reaction kinetics in MgO-based cements. However, little is known about the influences of organics on the formation pathways of carbonate phases and whether organo-modified Mg‑carbonates exist. We found that acetate can be involved in the formation of a new hydrated magnesium carbonate phase containing acetate: [Mg₅(CO₃)_3.25(OH)₂(CH₃COO)_1.5·5H₂O]. In this work, the solubility product (log K_s0) of this phase was reported for the first time, while we also re-calculated the log K_s0 of artinite. This acetate-containing giorgiosite is rather stable at low temperature but artinite [Mg₂(OH)₂(CO₃)(H₂O)₃] and amorphous magnesium carbonates were observed at 20 °C while hydromagnesite [Mg₅(CO₃)₄(OH)₂·4H₂O], hydrated carbonate brucite (HCB) and amorphous magnesium carbonates were present at 50 and 80 °C. The work enables the potential of using organic additives in steering the reaction and formation of carbonates for better efficacy of carbon utilization and reactions in MgO-based cements.